Falls affect millions of people each year and result in significant injuries, particularly among the elderly. In fact, it has been estimated that falls are one of the top three causes of death in elderly people. A fall can be defined as a sudden, uncontrolled and unintentional downward displacement of the body to the ground followed by an impact.
Personal Help Buttons (PHBs) are available that require the user to push the button to summon help in an emergency. However, if the user suffers a severe fall (for example if they are knocked unconscious), the user might be unable to push the button, which might mean that help doesn't arrive for a significant period of time, particularly if the user lives alone.
Fall detectors are also available that process the output of one or more movement sensors to determine if the user has suffered a fall. However, it has been found that these fall detectors have an unfavorable trade-off between fall detection probability and false alarm rate.
Given that a high false alarm rate will result in additional costs to the organization responsible for giving assistance to the user of the fall detector (i.e. they will need to contact or visit the user of the fall detector when the fall detection alarm is triggered) and that a high false alarm rate is undesirable for the user of the fall detector, it has been found that an economically viable fall detector should provide a false alarm rate of, say, less than one false alarm in each two-month period, while maintaining a (positive) fall detection probability above 95 percent.
Most existing body-worn fall detectors make use of an accelerometer (usually a 3D accelerometer that measures acceleration in three dimensions) and they try to infer the occurrence of a fall by processing the time series generated by the accelerometer.
In particular, a fall detector can estimate a velocity and/or displacement for the fall detector from the accelerometer measurement samples and use these features (along with other features derived from the accelerometer measurement samples) to determine whether the user of the fall detector has suffered a fall.
It is desirable to provide fall detectors in the form of pendants that can be worn around a user's neck and that is otherwise free to move relative to the user; as such fall detectors are lightweight and unobtrusive in use. However, existing methods for estimating the vertical velocity and vertical displacement do not provide sufficiently accurate estimates when applied to measurement samples obtained from an accelerometer in this type of fall detector.
Therefore, there is a need for an improved method for estimating vertical velocities and/or vertical displacements from accelerometer measurement samples.